1. Field of the Invention
The present invention relates generally to the field of tracking, monitoring, and analyzing movement of a rigid body in three dimensions in relation to another body as they both move in relation to a motion detector, and more specifically to the tracking, recording, monitoring, analyzing, and displaying the movement of a mandible in relation to a cranium.
2. State of the Prior Art
The field of dental occlusion (closure of the jaws) is many-faceted and has many implications, some of which researchers and practitioners have only recently become aware, and such awareness is still growing. For example, disfunctions of the temporal mandibular joint (TMJ) can be manifested in such a widely varying symptoms as pain or noise in the TMJ itself, headache, backache, vision impairment, and others. Therefore, it has become important to be able to classify TMJ disfunctions for more effective analysis and treatment and to be able to monitor the effects of TMJ treatment. Other applications in this field of dental occlusion include rehabilitation of the occlusion by restorative, orthodontic, and/or surgical means, as well as the construction of prosthetic devices.
The problem of measuring and analyzing the physical relationship between the upper and lower jaws during the processes of speech, mastication (chewing), and deglutition (swallowing) is crucial to this field and study of dental occlusion. For example, the following relationships and motions are significant to researchers and practitioners working in this field:
(1) Envelopes of motion of the mandible during normal speech and chewing, and during maximum extension.
(2) Movement of the condyles within envelopes of possible movement as the patient chews, speaks, or swallows.
(3) Similarities and differences in condyle displacement between rest position and "centric relation" in different individuals.
(4) Mandibular velocities during various functions.
(5) Asymmetries of movement during functional activity.
(6) Changes in functional activity and border movement after various types of therapeutic intervention.
Mechanical articulators have been used to advance knowledge of relative jaw movement. See, e.g., B. B. McCollum, "Gnathology, A Research Report," Scientific Press, Pasadena, Calif. (1955), and by W. G. A. Bonwill, The Scoentific Articulation of the Human Teeth as Founded on Geometrical, Mathematical, and Mechanical Laws, 8 J. PROSTHETIC DENTISTRY 41 (1958). An empirical approach published by N. G. Bennett, A Contribution to the Study of the Movements of the Mandible, 21 DENT. ITEMS OF INTEREST 617 (1899), was another important early step in this field. L. E. Kurth, Centric Relations and Mandibular Movement, 50 JADA 309 (1955), B. Jankelsen, Physiology of the Human Dental Occlusion, 50 JADA 664 (1955), and U. Posselt, "Physiology of Occlusion and Rehabilitation", F. A. Davis Co., Blackwell Scientific Publication, Philadelphia, at 44 (1962), were more functionally oriented studies of dental occlusion. A significant report in which the limits of movements of the condyle heads were defined by using a series of wax check bites with the teeth held in different positions of opening and eccentricity is found in U. Posselt, Movement Areas of the Mandible, 7 J. PROSTHETIC DENTISTRY 368 (1957).
While all of the developments described above represented significant advances in the study and understanding of dental occlusion, they were based on methods that used bulky intra-oral mechanical components to acquire mandibular movement data. Such bulky, cumbersome instrumentation introduced distortions into the masticatory (chewing) pattern resulting in data that was somewhat skewed from a person's normal mandibular movement patterns. Also, the data were not stored and were not available for subsequent analysis.
Consequently, more recent efforts in this field have moved in the direction of trying to gather more accurate data for occlusion analysis. One such development utilizes a magnet mounted on a patient's tooth, and a system of antennae positioned on either side of the patient's head pick up signals indicative of the tooth. However, this type of system is limited to tracking a single point. Therefore, three-dimensional movements of the entire mandible cannot be determined.
Another type of system uses rigid stylii, attached to the mandible, which move against a resistive foil recording surface. A variation of this kind of system uses three styli attached to the teeth and three orthogonal sensor surfaces. See S. Hobo & S. Mochizuki, A Kinematic Investigation of Mandibular Border Movement by Means of an Electron Measuring System, Part I: Development of the Measuring System, 50 J. PROSTHETIC DENTISTRY 368, No. 3 (1983), and S. Hobo, A Kinematic Investigation of Mandibular Border Movement by Means of an Electronic Measuring System, Part II: A Study of the Bennett Movement, 51 J. PROSTHETIC DENTISTRY 642, No. 5 (1984). This kind of system is quite constraining to the patient, and computation of condylar paths is slow.
Researchers in this field are now recognizing that recording and display of mandibular movements should be performed on a real-time basis in order to have real clinical utility. The approach to the mandibular movement problem considered to be the most flexible at the present time involves the tracking of light emitting diodes (LED's) on the mandible using various kinds of detectors. These LED tracking systems can produced three-dimensional coordinates that can be plotted in various planes, displayed graphically on a computer monitor, and stored for later analysis.
There are a number of variations in the mean of attaching the LED's to the mandible and in the types of detection and computing hardware employed. For example, a single LED on a patient's mandible has been used. See T. Jemt, Chewing Patterns in Dentate and Complete Denture Wearers Recorded by Light Emitting Diodes, 5 SWED, DENT. J. 199 (1981), S. Karlsson, Recording of Mandibular Movements by Intra-orally Placed Light Emitting Diodes, 35 ACTA. ODONT. SCAN. 111 (1977), and A. Ekfeldt, T. Jemt & L. Mansson, Interocclusal Distance Measurement Comparing Chin and Tooth Reference Points, 47 J. PROSTHETIC DENTISTRY 560, No. 5 (1982). Another approach uses clutch-mounted (fastened to teeth) LED's and three linear array detectors with 2,048 diodes on each detector, and three-dimensional coordinates are computed by a specialized hardware interface and displayed on a graphics screen. See F. Mesqui, F. Kaeser & P. Fisher, On-line Three-dimensional Light Spot Tracker and Its Application to Clinical Dentistry, PROCEEDINGS, BIOSTERIOMETRICS, at 310 (1985), and S. Palla, B. Ernst & F. Mesqui, The Condylar Path of Clicking Joints, IADR ABSTRACT 145 (1986).
The present inventors also reported the use of a non-restraining head harness comprises of an upper component mounted on the cranium and a lower component mounted on the lower jaw and fastened together by elastic connectors. Three LED's were mounted on the upper component, and three LED's were mounted on the lower component. The LED positions were detected by two detectors and computed in three dimensions using photogrammetric techniques. See S. Curry & S. Baumrind, Real Time Monitoring of the Movement of the Mandible, 4 PROCEEDINGS, AMERICAN SOCIETY OF PHOTOGRAMMETRY 99 (1986). These developments, while significant in some sense, also highlighted the substantial shortcomings of the then-existing technology.
In spite of the work and studies described above, all of which have incrementally advanced the state of this art prior to this invention, there still remained a need for additional improvements to attain a system that would monitor the movements of the human mandible more accurately and more efficiently in three dimensions. For example, in order to obtain more realistic, natural results, the patient needs to be allowed maximum freedom of movement with a minimum of constraint on his/her natural head movement activity, yet the detectors must be able to detect the mandibular movement accurately, in spite of such freedom of movement. The LED's have to be mounted in more secure, immoveable, and stable relation to the patient's lower jaw and cranium, yet maintain maximum comfort and minimum constraint against movement. More accurate and efficient data processing and controls, as well as improved and useable displays of results, are imperative for any feasible and useful application. Also, improved tracking of individually selected points, as well as an ability to find or pinpoint specific desired points in a predictable, repeatable manner were still required prior to this invention, as well as an ability to repeat measurements of specific points, axes of rotation, and the like, at a later date, and compare them to prior data.